This invention relates generally to inkjet printing mechanisms, and in particular to techniques for maintaining inkjet printhead at its optimal conditions.
Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as xe2x80x9cink,xe2x80x9d onto a media sheet. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the media sheet, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezoelectric or thermal printhead technology.
To clean and protect the printhead, typically a xe2x80x9cwiper assemblyxe2x80x9d mechanism is mounted within the housing of the printing mechanism so the printhead can be moved over the assembly for maintenance, specifically for wiping off ink residues and any paper dust or other debris that have collected on the printhead.
Normally, a wiping sequence includes a forward and a backward wiping stroke. During the forward stroke, a wiper blade of the wiper assembly moves from its home position, which is in front of the printhead in a media advancement direction, towards the other end of the printhead until it has passed the other end for wiping off ink residues on the printhead. After the forward stroke, the wiper blade moves from a position behind the printhead in the media advancement direction to its home position during the backward stroke; wiping also occurs during such a backward stroke.
The wiper blade normally has two sides at its wiping end for wiping the printhead during the forward and backward strokes respectively. During the forward stroke, most ink residues on the printhead are wiped off, and one side of the wiper blade""s wiping end becomes wet due to the ink residues. However, the other side of the wiper blade""s wiping end remains dry due to the fact that it is not in contact with the inks on the printhead during the forward stroke. Therefore, when the other side of the wiping end wipes the printhead during the backward stroke, a dry wiping of the printhead occurs if no other fluids are used to moisten the wiper blade. Such a dry wiping of the printhead may not be desirable in that it may increase the risk of damaging the nozzles on the printhead and the wiper blade itself.
Solutions have been introduced to solve such a problem. For example, some fluids can be used to wet the wiper blade before the backward stroke starts. However, such a solution can be relatively complicated because more parts and more complicated coordination between these parts are required to wet the wiper blade.
Therefore, there is a need for an improved printhead wiping mechanism which reduces the risk of damaging the printhead during the backward stroke of a wiping process more conveniently.
According to an aspect of the present invention, a method for wiping a printhead of an inkjet printing mechanism is provided. During a wiping process, firstly, a first amount of wiping force is exerted on the printhead for wiping the printhead in a first direction. Subsequently, a smaller amount of wiping force is exerted on the printhead for wiping the printhead in a second direction opposite to the first direction. The potential damages on the printhead by a dry wiping can thus be decreased by controlling the wiping force on the printhead.
According to a second aspect of the invention, a wiper assembly is provided for wiping a printhead of an inkjet printing mechanism having a chassis, with the printhead on a carriage supported by the chassis for moving to a wiping position. The wiper assembly includes a guide track mounted to the chassis, a platform movable along the track in a forward and a backward direction during a forward and a backward wiping stroke respectively, and a wiper blade mounted on the platform for wiping the printhead when the printhead is in the wiping position. A character of the wiper blade can be adjusted so that the wiper blade exerts different amounts of wiping forces on the printhead during the forward and the backward strokes.